Aluminum foil or band with an electrically insulating or decorative coating thereon and a method for producing the same

ABSTRACT

An aluminum foil, band or the like with the electrically insulating or decorative coating applied to the outer surface thereof and comprising an inner oxide layer and an outer lacquer layer and a method and apparatus for producing the coated foil or the like in a continuous manner by passing the foil first through an electrolytic anodizing means for producing the oxide layer and subsequently through an electrophoresis device for applying the lacquer layer onto the oxide layer.

United States Patent [72] Inventors I-Ielmut Friedrich Herrmann [54]ALUMINUM FOIL OR BAND WITH AN ELECTRICALLY INSULATING OR DECORATIVECOATING THEREON AND A METHOD FOR PRODUCING THE SAME 2 Claims, 3 DrawingFigs.

[52] US. Cl 204/28, 204/58, 204/207 51 nt. Cl C23b 9/02,

C23b 13/00, BOlk 5/00 [50] Field of Search 204/28, 38 A, 58, 425,181

[56] References Cited UNITED STATES PATENTS 2,215,165 9/1940 Sumner204/181 X 2,538,317 l/l951 Mason et al. 204/28 2,901,412 8/1959Mostovych et al.. 204/58 X 3,274,078' 9/1966 Tsuji 204/38 A X FOREIGNPATENTS 656,566 2/l938 Germany 204/181 Primary Examiner-F. C. EdmundsonAttorney-Michael S. Striker ABSTRACT: An aluminum foil, band or the likewith the electrically insulating or decorative coating applied to theouter surface thereof and comprising an inner oxide layer and an outerlacquer layer and a method and apparatus for producing the coated foilor the like in a continuous manner by passing the foil first through anelectrolytic anodizing means for producing the oxide layer andsubsequently through an electrophoresis device for applying the lacquerlayer onto the oxide layer.

60 www I 68 mama] m1 1 ma Y 3334.206

INVENTOR HELMUT FRIEURIEH HERRMANN BY RULANUU mmznu W l/4d 5.. ffmlwtheir ATTORNEY ALUMINUM FOIL OR BAND WITH AN ELECTRICALLY INSULATING RDECORATIVE COATING THEREON AND A METHOD FOR PRODUCING THE SAMEBACKGROUND OF THE INVENTION The present invention relates to an aluminumfoil, band or the like with an electric insulating or decorative coatingthereon, as well as to a method and apparatus for continuously producingthe aluminum foil or the like with the coating thereon.

It has been known for a considerable length of time that aluminum foilsor bands can be used as electrical conductors for instance in bandspools, condensers, and similar devices. For this purpose the foil orband is provided with an electrically insulating coating applied to theouter surface thereof. It is further known that an oxide layer appliedto the outer surface of the band or foil forms a good electricalinsulator and has in addition other advantageous characteristics. It isalso known that such an oxide layer is porous and that the pores of thelayer may be filled in various ways with organic or inorganic matterwhich may include foreign metals, organic pigments or inorganicprecipitations. It is also known to provide a layer of lacquer as anelectric insulation on wires or the like. Finally, the anodic depositionof organic matter by electrophoresis is also known. Electrophoresis isknown for depositing of lacquers of different kind for providing aprotective coating as well as for obtaining decorative effects.

It is an object of the present invention to provide an aluminum foil orband with an electric insulating and/or decorative coating havingimproved insulating and tenacity characteristics as compared with suchcoatings known in the art.

It is a further object of the present invention to provide for a methodof forming such a coating on an aluminum foil or the like in acontinuous and efficient manner and to provide also for an apparatus forcarrying out the method of the present invention.

SUMMARY OF THE INVENTION The present invention is based on the newrecognition that an aluminum foil or the like which is, subsequent to anelectrolytical oxidation for the production of an oxide layer thereon,provided with a lacquer layer by electrophoresis, has electricalcharacteristics which surprisingly are better than the sum of theelectrical characteristics which would be normally expected by thecommon application of the two method steps.

The present invention is on the one hand directed to an aluminum foil orthe like with an electrically insulating and/or decorative coating andcomprising an inner electrolytically produced oxide layer and an outerlacquer layer applied by electrophoresis to the inner oxide layer.

In this way, an electrically insulating coating is obtained whichcombines a surprisingly high-insulation coefficient with an excellentmechanical strength and a perfect binding of the coating to the basematerial. When used as decorative coating, it is characterized by itssturdiness, stability and a perfect aesthetic appearance.

0n the other hand, the present invention is also directed to a methodfor producing such an aluminum foil or the like in which the two layercoating may be produced in a single continuous process.

The method according to the present invention mainly comprises the stepsof continuously passing an elongated metal foil or the like consistingessentially of aluminum or aluminum alloy through an electrolytic meanscomprising at least two adjacent chambers containing an electrolyte andeach equipped with an electrode connected to an alternating currentsupply for producing an oxide layer on the outer surface of the foil,whereby the foil forms during its passage through the chambers a bipolarconductor, rinsing the oxide layer downstream of the electrolyte meansand subsequently passing the foil with the rinsed oxide layer thereonthrough an electrophoresis bath to apply to the oxide layer an outerlacquer layer. The method may further include the step of rinsing theouter layer downstream of the electrophoresis bath and subsequentlydrying the outer lacquer layer and burning in the same whilecontinuously moving the foil in longitudinal direction.

With the method according to the present invention it is thereforepossible to provide an aluminum foil or band in a single continuousprocess, which may be carried out automatically, with an electricallyinsulating outer coating comprising an inner oxide. layer and a lacquerlayer applied by electrophoresis thereto.

The present invention includes also an apparatus for carrying out theabove-described method and including electrolytic anodizing means, anelectrophoresis bath, means for guiding the electrofoil or band throughthe anodizing means and the electrophoresis bath in a continuous manner,and means for rinsing the foil after leaving the anodizing means as wellas after leaving the electrophoresis bath, for drying the foil after thesecond rinsing, and eventually also means for burning in the lacquerlayer applied to the oxide layer.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a cross-sectional view of analuminum band provided with the insulating and decorative layer thereon,and drawn to a greatly enlarged scale;

FIG. 2 is a schematic view of an apparatus for carrying out the methodof the present invention; and

FIG. 2a is a partial view of a slight modification of the apparatusshown in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a crosssection through an aluminum band 10 provided with an insulating ordecorative coating 12 according to the present invention, and forclaritys sake, the thickness of this coating is exaggerated in FIG. 1.The coating 12 consists of an inner oxide layer produced by anelectrolytic anodizing process onto the outer surface of the band 10 andof an outer lacquer layer 16 applied by electrophoresis to the inneroxide layer. The oxide layer 14 is porous and is intimately bound to thebase material 10 which essentially consists of aluminum or aluminumalloy. During application of the outer lacquer layer by electrophoresisonto the oxide layer 14, the lacquer particles are also deposited in thepores of the oxide layer 14 so that an intimate bond between the oxidelayer 14 and the lacquer layer 16 will result. Due to the application ofthe lacquer layer by electrophoresis onto the inner oxide layer 14, thelacquer layer 16 will be formed heavier on those portions of the oxidelayer at which the latter, due to its porosity or for other reasons hasa smaller insulating capacity, since due to the greater potentialdifference at this location more lacquer particles are depositedthereon. The production of the lacquer layer by electrophoresisconstitutes therefore at the same time a test for the quality of theoxide layer 14, whereby eventually existing faults in the oxide layerare automatically corrected by increased accumulation of lacquerparticles.

The method according to the present invention shall now be explained inconnection with FIG. 2 schematically illustrating an apparatus forcarrying out the method. This apparatus includes a supply roll 20 onwhich an aluminum foil or band 22 consisting essentially of aluminum oran aluminum alloy is wound up and the aluminum band or foil 22 is guidedover a guide roller 24 into an electrolytic anodizing device 26 which,in the embodiment illustrated, comprises two chambers 28 and 30separated from each other by a central wall 34. The aluminum band 22enters first into the chamber 28 and is guided through the electrolytetherein by a guide roller 32 adjacent to the bottom wall of the chamber28 and leaves the latter over a guide roller 36 turnably mounted at theupper end of the central wall 34 to enter into the second chamber 30 andis passed through the electrolyte therein by a guide roller 38 adjacentto the bottom wall of the second chamber, from which the aluminum band22 is guided over a roller 40 at the end of the second chamber. Astationary electrode 42, respectively 44, is arranged in each of thechambers 28 and 30 in such a manner that the lower end of each electrodedips into the electrolyte respectively contained in these chambers andis out of direct contact with the aluminum band guided therethrough. Theouter ends of the electrodes 40 and 44 are connected to a supply ofalternating current 46 as schematically illustrated in FIG. 2. Theportions of the band 22 respectively located in the electrolyte ofchambers 28 and 30 form thereby a bipolar conductor.

The anodizing means 26 may also comprise more than two chambers.Likewise, instead of guiding the aluminum band 22 in a meanderingmanner, as shown in FIG. 2, through the electrolyte in the two chambers28 and 30, it is also possible to guide the band along a straight paththrough the electrolyte in the two chambers, whereby the outer walls andthe central wall 34 of the anodizing means 26 are formed withcorresponding slots provided with sealing means for guiding the band 22along a straight path and in a sealed manner through the electrolytescontained in the two chambers. The illustrated anodizing means 26 istherefore only a nonlimiting example of a multichamber alternatingcurrent anodizing apparatus in which the band passing therethrough formsa bipolar conductor.

During passage of the band 22 through the anodizing means 26, the bandwill be provided with an oxide layer thereon due to the knownelectrochemical processes occurring during the passage of the bandthrough the anodizing means, which electrochemical processes are knownand need therefore not be discussed in detail.

After leaving the anodizing means 26, the band 22 is passed through arinsing device 48, of known construction and only schematicallyillustrated in FIG. 2, in which the oxide layer provided on the band 22is thoroughly rinsed. Evidently, it is also possible to provide betweenthe supply roll 20 and the anodizing device 26 means for cleaning thealuminum band 22 before the latter enters the anodizing device, if suchshould be necessary.

The aluminum band 22 provided with the oxide layer on the outer surfacethereof is passed after the rinsing device 48 into an electrophoresisdevice 50 which comprises a container 52 in which a bath S3 ismaintained. The band 22 is guided about a guide roller 58 turnablymounted in the region of the upper end of one end wall of the container52 and through the bath 53 by means of two guide rollers 56 adjacentopposite end walls of the container and to the bottom wall thereof toleave the bath over a guide roller 58 turnably mounted in the region ofthe other end wall of the container. An electrode 60 is arranged in thebath 53 in the container 52 out of direct contact with the band 22 whichis guided through the bath and the electrode 60 is connected to theminus pole ofa direct current supply, not shown in the drawing. The band22 itself is connected to the plus pole of this direct current supply.Since the oxide layer applied in the anodizing device 26 to the aluminumband is an insulating layer, it is necessary to make the connection ofthe plus pole of the direct current supply to the band 22 before theoxide layer is applied thereto. For this purpose, the positive pole ofthe direct current supply may be connected directly to the supply roll20 as schematically indicated in FIG. 2a, or preferably by a contactroll 54 engaging the band 22 between the supply roll 20 and the guideroller 24 on the anodizing device 26, and the contact roller 54 is thenconnected to the positive pole of the direct current supply asschematically shown in FIG. 2.

The bath 53 maintained in the container 52 essentially consists of waterin which to 12 percent by volume oflacquer or color particles aredispersed which due to their contact with the negatively chargedelectrode 60 are likewise negatively charged to be attracted by thepositively charged band 22 so that the particles will not only form athin outer layer on the oxide layer, but will also penetrate the poresof the oxide layer. The electrochemical processes occurring during thiselectrophoresis are well known and a further description thereof seemstherefore not necessary.

After leaving the guide roller 58, the aluminum band 22 with the coating12 comprising the inner oxide layer and the lacquer layer appliedthereto is then passed through an additional rinsing means 62 of knownconstruction, through drying means 64 schematically illustrated in FIG.2, and through a burning-in device 66, of known construction and onlyschematically shown in FIG. 2, to be finally wound up by the windupdevice 68 which is driven continuously by means not shown in thedrawing.

The electrolyte in the chambers 28 and 30 of the electrolytic anoidizingmeans 26 consists essentially of an aqueous sulfuric acid of aconcentration of 20 percent by volume and this electrolyte is preferablymaintained at a temperature of 40 C.

The anodic treatment of the aluminum band is carried out preferably at acurrent density of about 50 amperes per I00 square centimeters. The bathmaintained in the electrophoresis device 50 essentially consists ofwaterwith 10 to 12 percent per volume lacquer or color particles dispersedtherein and the electrophoresis is preferably carried out with a currentdensity of 0.3 ampere per square centimeters. The windup means 68 ispreferably driven with such speed that the anodic treatment of the bandin the anodizing means 26 as well as the electrophoresis in the device50 is carried out for a time of about 12 seconds.

According to the present invention the aluminum band 22 is thereforeprovided with a two-layer coating in a continuous automatic process inwhich in the device 26 is a porous oxide layer is applied to the outersurface of the aluminum band and in the device 50 a lacquer layer isapplied to the oxide layer whereby die to the electrophoresis thelacquer particles will also be disposed in the pores of the porous oxidelayer.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofaluminum foil or band with an electric insulating and decorative coatingand a method for producing the same differing from the types describedabove.

While the invention has been illustrated and described as embodied inaluminum foil or band with an electric insulating or decorative coatingand a method for producing the same, it is not intended to be limited tothe details shown, since various modifications and structural changesmay be made without departing in any way from the spirit ofthe presentinvention.

Obviously, it is also possible to subject the aluminum band to furthertreatment and it is also possible to use instead of the burning-in means66 a different device in order to fix the lacquer layer to the oxidelayer.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:

1. A continuous method of producing an aluminum foil or band with anelectrically insulating and decorative coating applied to the surfacethereof and comprising an inner porous oxide layer and an outer lacquerlayer which fills the pores of said inner oxide layer to thus obtain aperfect bond between said layers, said method comprising the steps ofcontinuously passing an elongated body such as a band or foil consistingessentially of aluminum or aluminum alloy through an electrolytic meanscomprising at least two adjacent chambers containing electrolyte andeach equipped with an electrode connected to an AC current supply forproducing a porous oxide layer on the outer surface of said elongatedbody, whereby the latter forms during its passage through said chambersa bipolar conductor; connecting said elongated body upstream of saidelectrolytic means to the positive pole ofa DC current supply; rinsingsaid oxide layer downstream of said electrolytic means; and continuouslypassing said elongated body with said rinsed layer thereon through anelectrophoresis bath equipped with an electrode connected to thenegative pole of said DC current supply to apply to said porous oxidelayer an outer lacquer layer by electrophoresis so that said lacquerlayer penetrates also into the pores of said oxide layer.

2. A method as defined in claim 1 and including the steps of 5

2. A method as defined in claim 1 and including the steps of rinsingsaid outer layer downstream of said electrophoresis bath andsubsequently drying said outer lacquer layer and burning-in said outerlacquer layer while continuously moving said elongated body inlongitudinal direction.